The present invention relates to a melt spinning method and an apparatus used in the method for manufacturing a nonwoven fabric by supplying, onto a conveyor belt, fibers formed by extruding melted resin by using a melt blowing method.
The melt blowing method is a melt spinning method for obtaining a nonwoven fabric sheet from fibers (threads) obtained by melting and extruding raw resin. By the melt blowing method, melted resin is cast into a mold and extruded by an extruder from a nozzle of the mold and, simultaneously, supplied with hot and high velocity airflow from the periphery of the nozzle so that the melted resin may be discharged into fiber shapes (threads). The fibrous resin is supplied onto a conveyor, to manufacture a nonwoven fabric sheet.
As for this type of spinning method, for example, a laterally arranged web manufacturing method is known which is disclosed in Japanese Laid-Open Patent Publication No. 2001-98455. That is, the method includes a step of extruding melted resin from a spinning nozzle into the shape of fibers; a step of discharging hot primary air from the periphery of the open end of the spinning nozzle to vibrate the fibrous melted resin; a step of discharging hot secondary air toward the fibrous melted resin as it vibrates and falls, so that the resin may be spread in a widthwise direction and spun; and a step of laminating the fibrous melted resin onto a conveyor to manufacture laterally arranged webs.
However, the manufacturing method described in the above publication aims at obtaining webs arranged laterally, so that it is necessary to vibrate fibrous melted resin extruded from a spinning nozzle by using primary air and spread it in a widthwise direction by using secondary air. Specifically, a stream of primary air is discharged at a high velocity to form depressurized portions in the peripheral portion of the melted resin in the form of the fibers, which have been extruded from the spinning nozzle, thus vibrating the melted resin. This makes it difficult to orient the molecules of the melted resin in the same direction. The fibers thus have a decreased strength and are easily cut. Further, a stream of secondary air is discharged laterally to the melted resin, thus causing turbulence in the stream of the melted resin in the form of the fibers. The fibers are thus cut easily. As a result, it is difficult to form the melted resin in the form of thin and uniform fibers.